1. Field of the Invention
The present invention relates to a capacitor mounting type inverter unit for controlling a driving motor in an electric vehicle or a hybrid vehicle, for example.
2. Description of the Related Art
A capacitor mounting type inverter unit includes a smoothing capacitor for smoothing a voltage from a high-voltage battery, three phases of switching modules (which will be hereinafter referred to as “SW modules”) for outputting a three-phase AC voltage according to an output voltage from the smoothing capacitor, a SW module control board for controlling the switching of the SW modules, and an electronic control unit (which will be hereinafter referred to as “control ECU”) for controlling the SW module control board. The combination of the SW modules and the SW module control board will be hereinafter referred to as “inverter”, and the combination of the inverter and additional components including the smoothing capacitor will be hereinafter referred to as “inverter unit”. Related structures of such a capacitor mounting type inverter unit are described in the following Related arts 1, 2, and 3, for example.
FIG. 18 is a perspective view showing the structure of a capacitor mounting type inverter unit 212a described in Japanese Patent Laid-open No. 2000-152662 as Related art 1. The inverter unit 212a includes a smoothing capacitor 213a and an inverter 215a formed independently of the smoothing capacitor 213a. The smoothing capacitor 213a is fixedly mounted on the inverter 215a by screws. The smoothing capacitor 213a is retained by a capacitor retaining component 280a. 
The smoothing capacitor 213a is connected to positive and negative electrodes through input terminal bases 208a#P and 208a#N formed on the inverter 215a and bus bars 214a#P and 214a#N formed through an insulating member. The inverter 215a is connected to the input terminal bases 208a#P and 208a#N through bus bars formed independently of the bus bars 214a#P and 214a#N. Further, current sensors are connected through dedicated bus bars to output bus bars of the inverter.
FIG. 19 is a circuit diagram showing Related art 2. As shown in FIG. 19, input lines 202b#P and 202b#N are connected to the positive and negative electrodes of a battery 200b, respectively. Reference numeral 206b generally denotes a noise absorbing capacitor having two capacitors 250b. The positive electrode of one of the capacitors 250b is connected through a lead wire 252b#P, a conduction board 253b, and a bus bar 254b#P to the input line 202b#P. The negative electrode of the other capacitor 250b is connected through a lead wire 252b#N, the conduction board 253b, and a bus bar 254b#N to the input line 202b#N. The other electrodes of the capacitors 250b are grounded through a lead wire 256b, a conduction board 257b, and a ground line 258b. 
Reference numeral 212b generally denotes an inverter unit having input terminal bases 208b#P and 208b#N, a smoothing capacitor 213b, input bus bars 214b#P and 214b#N, SW module input bus bars 216b#P and 216b#N, SW modules 222b#i (i=1, 2, 3), a SW module control board 228b, a control ECU 230b, and output terminal bases 231b. 
The input terminal bases 208b#P and 208b#N are connected to the input bus bars 214b#P and 214b#N, respectively. The smoothing capacitor 213b is connected through lead wires 260b#P and 260b#N and a conduction board 261b to the input bus bars 214b#P and 214b#N. The SW modules 222b#i (i=1, 2, 3) are connected through the input bus bars 216b#P and 216b#N to the input bus bars 214b#P and 214b#N.
The output terminal bases 231b are connected through output bus bars 274b#i (i=1, 2, 3) to SW module output bus bars 270b#i (i=1, 2, 3). A motor 236b is connected through output lines 234b to the output terminal bases 231b. Current sensors 232b#i (i=1, 2, 3) are provided so that the output lines 234b extend through the current sensors 232b#i (i=1, 2, 3) for the purpose of detecting currents flowing in the output lines 234b. The SW modules 222b#i (i=1, 2, 3) are controlled through the SW module control board 228b by the control ECU 230b. 
FIGS. 20 to 30 show the structure of the capacitor mounting type inverter unit 212b in Related art 2 mentioned above. As shown in FIG. 20, the inverter unit 212b is covered with a separate cover 300b. The inverter unit 212b is connected to the noise absorbing capacitor 206b as a separate component. As shown in FIG. 21, the smoothing capacitor 213b is accommodated in a capacitor holding stay 302b. The smoothing capacitor 213b is composed of a plurality of capacitors, each of which is connected to a lead wire 260b shown in FIG. 22, surrounded by a potting resin 310b, and held by a capacitor holding case 312b. As shown in FIG. 23, the smoothing capacitor 213b is connected through the lead wires 260b and the conduction board 261b to the input bus bars 214b#P and 214b#N.
As shown in FIGS. 21 and 24, the smoothing capacitor 213b, the SW modules 222b, and the SW module control board 228b are accommodated in an inverter case 304b independent of the inverter cover 300b. As shown in FIG. 25, each SW module 222b is connected to the corresponding SW module input bus bars 216b#P and 216b#N and the corresponding SW module output bus bar 270b. As shown in FIG. 26, the SW module input bus bars 216b#P and 216b#N are connected to the input bus bars 214b#P and 214b#N, respectively. Each SW module output bus bar 270b is connected to the corresponding output bus bar 274b, which is in turn connected to the corresponding output terminal base 231b. As shown in FIG. 27, the output lines 234b are inserted through the respective current sensors 232b#i (i=1, 2, 3) independent of the inverter unit 212b and fixedly connected to the respective output terminal bases 231b by screws 320b. 
As shown in FIGS. 28 and 29, the noise absorbing capacitors 250b are partially covered with a potting resin 352b and held in a holding case 350b. The opposite electrodes of the cascaded noise absorbing capacitors 250b are connected through the lead wires 252b and the conduction board 253b to the bus bars 254b. The holding case 350b is accommodated in a case 356b independent of the inverter unit 212b. The bus bars 254b are connected to terminals of the case 356b, and a ground harness 258b is connected to a terminal 358b of the case 356b. 
FIGS. 31 and 32 show the structure of a capacitor mounting type inverter unit 212c in Related art 3. As shown in FIG. 31, a smoothing capacitor 213c is held and accommodated in a holding component 320c. The electrodes of the smoothing capacitor 213c are connected through a bus bar 214c to SW modules. The output bus bars of the SW modules are connected through output lines 234c to output bus bars 274c. The output bus bars 274c are connected through current sensors 232c to output terminal bases 231c. The output lines 234c are connected to the respective output terminal bases 231c. The output terminal bases 231c are formed on a case independent of a case for accommodating the inverter unit 212c. As shown in FIG. 32, a noise absorbing capacitor 250c is formed independently of the smoothing capacitor 213c and is accommodated in a case 350c. The noise absorbing capacitor 250c is connected through bus bars 254c#P and 254c#N and a ground harness 258c to a terminal of a case 356c. 
In Related arts 1 to 3, however, the number of electrical connection parts such as lead wires and bus bars and the number of electrical connection points of such parts are large, causing an increase in electrical contact resistance, number of assembling steps, volume, weight, and cost. Further, in Related arts 1 to 3, it is necessary to provide dedicated components for holding the smoothing capacitor and the noise absorbing capacitor. Accordingly, the number of such capacitor holding components is large, causing an increase in number of assembling steps, volume, weight, and cost.
In the case that the current sensor is integrated with the inverter unit in Related art 1, it is necessary to provide a dedicated bus bar (bus bar between the inverter and the output line) for passing a current through the current sensor. In Related art 3, the current sensors 232c are formed independently of the inverter unit as shown in FIG. 31, and the bus bars 274c and the output terminal bases 231c are therefore necessary.
In the case that no bus bars like the bus bars 274c are set as shown in FIG. 27, it is necessary to perform the work of inserting the output lines 234c through the current sensors 232b and then fastening the output lines 234 to the output terminal bases 231b by using the screws 320b. Thus, Related arts 1 to 3 have the problem that the number of parts, the number of assembling steps, the volume, weight, and cost are increased.